Among conventional anti-skid control (ABS) apparatuses that increase/decrease the fluid-chamber capacity by means of linear movement caused by an electric motor, one proposed apparatus is a type in which an instruction current supplied to the motor is determined in accordance with a state variable corresponding to a motor speed as well as a tire slip rate (see Japanese Patent Application Laid-open No. HEI6-72312). This apparatus determines the instruction current supplied to the motor anticipating the speed energy provided by the motor in order to suppress the output from the actuator from overshooting a target value.
Further, in a linear electric disc brake which is operated by means of linear movement caused by an electric motor, an upper limit and a lower limit of the rotational speed of the motor are predetermined and the actual rotational speed of the motor is suppressed within the predetermined range (see Japanese Patent Application Laid-open No. 2003-104195).
However, in the apparatus disclosed in Japanese Patent Application Laid-open No. HEI6-72312, the higher the rotational speed of the motors is, that is, the faster the response is, the larger the resistance force (damping force) against the motor rotation becomes. Hence, the best use of the potential of the motor is not made. Accordingly, the following-up of the target value of the actuator output by the actual control variable is delayed, leading to a poor response.
In the brake apparatus disclosed in Japanese Patent Application Laid-open No. 2003-104195, suppression on the rotational speed of the motor makes it impossible to adequately use the potential of the motor. Accordingly, the following-up of the target value of the actuator output by the actual control variable is delayed, leading to a poor response.
Therefore, any apparatus used for brake control such as the two apparatuses disclosed in the related art is incapable of providing the response required for the brake control.
On the other hand, if the adjustment of the instruction current in accordance with the rotational speed of the motor or the setting of an upper limit and lower limit of the rotational speed of the motor is not executed, as in the cases of both apparatuses disclosed above in the related art, this may make it possible to provide a response corresponding to the potential of the motor. However, it is impossible to suppress an overshoot in which the output from the actuator exceeds or surpasses the target value, and/or hunting in which the output from the actuator attempts to converge on the target value resulting in an oscillation phenomenon. For this reason, a phenomenon occurs in which a large braking force is generated once and then rapidly drops. This phenomenon causes a driver to feel uncomfortable with braking, whereby a stable riding comfort is not provided.